Fossil polychaetes of the Lower Carnian limestone at Lesno Brdo, central Slovenia

Abstract

Lower Carnian massive limestone, quarried at Lesno Brdo in central Slovenia, contains irregular lenses of limestone riddled with fossil agglutinated tubes of Terebellida (Polychaeta). The aims of this study were to investigate changes in density and tube sizes within two of the lenses. Most of the tubes are oriented oblique or sub-parallel to former sea flor. They are embedded in fie-grained matrix or fragmented and overgrown by early diagenetic cement. Interiors of the tubes and larger voids within the matrix often display geopetal structures. We presume that lenses represent in situ populations of terebellid worms at the outer margin or upper slope of the former carbonate platform. For the larger of the two lenses, it seems that the tube density is largest at the bottom of the lens, whereas the density gets lower towards the top and the sides of the lens. The density distribution is more irregular in the second, smaller lens. We found no statistical correlation between the density and the size of the tubes. Grains, incorporated into the tube wall, match the composition of the surrounding sediment, meaning that the animals were not particularly selective for the grain type. The walls are also predominantly built of one grain size, irrespective of the size of the tube.

Keywords

• Polychaeta
• Terebellida
• Triassic
• External Dinarides
• carbonate platform
• reef